If you're pregnant—or trying to conceive—the Zika virus is probably a top-of-mind concern, and with good reason: This mosquito-borne virus can have potentially devastating consequences for pregnant women and their babies.

Zika has spread to nearly 100 countries throughout Africa, Asia, the Caribbean, Central America, the Pacific Islands, and South America. It has previously landed in the United States (although there have been no Zika transmission in the U.S. in 2018). The virus is likely to spread as well; check the CDC for areas at risk for Zika.

If you're expecting (and frankly, even if you're not), it's crucial to arm yourself with information and up-to-date advice. This is what you need to know.

What is Zika Virus?

The Zika virus is an insect-borne illness that can be primarily transmitted by infected Aedes mosquitoes, the same kind that carry dengue and yellow fever. The name comes from the Zika Forest in Uganda where monkeys with the virus were first found in 1947.

For the relatively few people who show signs of a Zika infection, the illness is often very mild. But in pregnant woman, the effects can be devastating, and can include pregnancy loss or a baby born with an abnormally small head and brain—a condition known as microcephaly, says Edward R.B. McCabe, M.D., Ph.D., Senior Vice President and Chief Medical Officer of the March of Dimes. Microcephaly may be associated with developmental delays, mental retardation, and seizures, and in some cases can be fatal.

Researchers have also found that the Zika virus can cause glaucoma in infants who were exposed in utero; it has also been linked to hearing loss, vision problems, and impaired growth in babies, according to the CDC. The full spectrum of outcomes for infants infected with Zika is still being studied, but we do know even babies who do not show initial signs of birth defects may develop progressive damage.

There are still many unknowns—including how likely it is that an infection in a pregnant woman will be passed on to her fetus; whether some fetuses are infected but don't develop microcephaly; how often pregnancy loss may occur in expecting women with Zika virus; and whether pregnancy makes women more susceptible to the virus, says Marjorie Treadwell, M.D., director of the Fetal Diagnostic Center at the University of Michigan and a maternal and fetal medicine expert.

While the Zika virus remains in the blood of an infected person for a few days to a week, according to the CDC, there's no current evidence to suggest that it poses a risk of birth defects in future pregnancies. And Zika won't cause infections in a baby that's conceived after the virus has left the bloodstream.

How is Zika Transmitted?

Zika is primarily spread through the bite of infected mosquitos. When a mosquito bites and draws blood from someone who's infected, the insect itself becomes infected and then goes on to bite other people.

Zika can also be transmitted sexually, through oral, vaginal or anal intercourse, according to the CDC. It can be spread from a man to a woman, and recently a possible case of a woman infecting a man was also reported. It’s important to note transmission can take place even if an infected person is not symptomatic.

The Zika virus can also be transmitted from mother to baby during pregnancy or around the time of birth, but according to the American College of Obstetricians and Gynecologists (ACOG), there are no clinical studies to measure the risk to an unborn child if the mother is infected. In rare instances, the Zika virus may be passed along via a blood transfusion, according to the CDC.

Zika virus has been detected in fetal tissue, amniotic fluid, full-term infants, and in the placenta, according to ACOG, and trace amounts of the virus have also been found in breast milk, but because the amount is tiny, it's unlikely to pose a threat.

Zika Virus Symptoms

A Zika infection is similar to a mild case of the flu and may include such symptoms as a low-grade fever, headache, rash, muscle and joint pain, and conjunctivitis (pink eye). Symptoms may last several days to a week. Only 20 percent of people infected with the Zika virus will actually become ill, reports Cynthia Moore, M.D., Ph.D., of the National Center on Birth Defects and Developmental Disabilities at the Centers for Disease Control and Prevention (CDC), adding, "We don't know at this time if pregnant women are more likely to develop symptoms if infected."

Testing for Zika Virus

The FDA still hasn’t approved a commercially available diagnostic test for Zika virus, but all pregnant women should be assessed for Zika at prenatal visits, according to the CDC. If you may have been exposed either during travel to an active Zika infection area, if you live in an active area, or if you could have been exposed through sexual contact, your doctor will order blood or urine tests to see if you are positive for the virus, even if you aren’t showing symptoms.

Specifically, the guidelines urge asymptomatic pregnant women who've been to places with known ongoing Zika transmission be tested between 2 and 12 weeks after they've returned—or right away if symptoms are present. The CDC also recommends that pregnant women without symptoms but who live in a Zika-affected area be tested for the virus at the start of prenatal care as well as later on, at the mid point of the second trimester. Even if you don't show signs, your unborn baby should be examined, usually via ultrasound. If there are concerns following an ultrasound, amniocentesis may be the next step.

Federal health officials are urging that newborns be tested if the mother has visited an affected area and also exhibits symptoms of the Zika virus. Your doctor should contact a health department for information about testing for Zika. Even if you don't show signs, your unborn baby should be examined, usually via ultrasound. If there are concerns following an ultrasound, amniocentesis may be the next step.

Reducing the Risk of Zika Virus

Guidance from the CDC now directs pregnant women to be very cautious when it comes to having sex with a partner who's traveled to a region affected by Zika.

Couples should use condoms during all forms of sex to reduce the risk of potential transmission or abstain entirely for the duration of the pregnancy. Even if you aren’t pregnant, it’s important to take precautions, especially if you are trying to conceive. Men who are showing symptoms and live in, or have traveled to an area where Zika is being locally transmitted should use condoms for six months; when the woman is infected, condoms should be used for 8 weeks.

There's no vaccine for Zika, but researchers from Florida State University, Johns Hopkins University and the National Institutes of Health have identified certain existing drugs that may be able to prevent the virus from replicating in the body and even protect fetal cells from being damaged. Most recently, it has been reported that scientists may have discovered an antibody that can help fight the virus. Clinical trials are currently being conducted.

Until a treatment has been proven effective, you can further reduce your risk by staying current with the latest recommendations. If you're pregnant, delay travel to the regions listed in the CDC's advisory (see below). If travel can't be avoided, take every precaution to avoid mosquito bites, including:

Wearing shirts with long sleeves and pants, rather than shorts

Using bug spray with DEET, which is safe for pregnant and nursing women (check the label and follow the directions carefully

Treating clothes with permethrin, a type of insecticide

Ridding your home of any free-standing water

If you aren't pregnant but have concerns because your male partner has been to a Zika-affected region, you can use condoms or abstain, notes the CDC. However, simply visiting the region isn't the only factor for contracting the disease. Risk also depends on a person's length of stay, how many mosquito bites he received and whether prevention measures were taken to prevent the bites.

For those couples who want to have a baby with a male partner who's recently traveled or lived in an exposed area, ask your doctor for advice. A Zika test may be possible but priority will first be given to women who are already pregnant.